Pyrene‐fused Acenes and Azaacenes: Synthesis and Applications

In this account, the synthesis and applications of pyrene‐fused acenes, as well as pyrene‐fused azaacenes, have been carefully reviewed. Moreover, the synthetic methods involving two key synthons (different lengths of dienes and ynes) have been included. Furthermore, the “clean reaction” strategy has been introduced for the preparation of pyrene‐fused acenes with a single terminal‐pyrene unit from tetracene to octacene, as well as for the synthesis of pyrene‐fused octatwistacenes and nonatwistacenes with double terminal‐pyrene units. Similarly, the synthons and the synthetic methods for pyrene‐fused azaacenes have also been summarized. The applications of pyrene‐fused acenes and pyrene‐fused azaacenes have been included.     

A quantum mechanical study of the abstraction reactions of fused bicyclic dimetallenes

The potential energy surfaces for the abstraction reactions of fused bicyclic dimetallene species with carbon tetrachloride have been characterized in detail by using density functional theory including zero-point corrections. All the stationary points were determined at the B3LYP/LANL2DZdp level of theory. Five fused bicyclic dimetallene species including fused bicyclic diethylene, fused bicyclic disilene, fused bicyclic digermene, fused bicyclic distannene, and fused bicyclic diplumbene have been chosen in this work as model reactants. Comparisons of the activation barriers and reaction enthalpies were used to determine the relative reactivity of the fused bicyclic dimetallenes on the reaction potential energy surface. As a result, our theoretical investigations suggest that, irrespectively of the fused bicyclic dimetallene, the Cl-abstraction pathway is more favorable than the CCl3-abstraction pathway from both kinetic and thermodynamic considerations. Moreover, our model calculations indicate that the heavier the group 14 element in the fused bicyclic dimetallenic species, the lower the activation barrier and the more exothermic the haloalkane abstraction. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.     

Strain Release of Fused Pentagons in Fullerene Cages by Chemical Functionalization

According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused‐pentagon‐containing (i.e. non‐IPR) fullerenes through an exhaustive review of all the types of fused‐pentagon‐containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in‐depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.     

Doubly N‐Fused [24]Pentaphyrin Silicon Complex and Its Fluorosilicate: Enhanced Möbius Aromaticity in the Fluorosilicate

Treatment of nonaromatic N‐fused [24]pentaphyrin with trichloromethylsilane in the presence of a base afforded doubly N‐fused [24]pentaphyrin and its silicon complex. Addition of fluoride ion to the silicon complex led to the formation of its fluorosilicate as an unprecedented monoanionic six‐coordinated Si^IV complex of porphyrinoid. Treatment of the fluorosilicate with acid led to the recovery of the silicon complex. The doubly N‐fused pentaphyrin, the silicon complex, and the fluorosilicate were all characterized as distinct Möbius aromatic molecules by spectroscopic measurements and X‐ray crystallographic analyses. Importantly, the second N‐fusion reaction, Si‐incorporation and fluoride addition to the Si‐atom enhanced the aromaticity of doubly N‐fused [24]pentaphyrins in this order. Tamao–Fleming oxidation of the silicon complex gave β‐keto doubly N‐fused pentaphyrin and triply fused [24]pentaphyrin, which were nonaromatic and Hückel anti‐aromatic, respectively.     

An efficient and selective route to hybrid trifluoromethyl-substituted γ-lactones or fused nitrogen derivatives via cascade reactions

A straightforward, efficient and selective route for obtaining hybrid trifluoromethyl-substituted γ-lactones and fused nitrogen heterocycles is presented. The reaction could be guided either to γ-lactones with a nitrogen-containing heterocyclic skeleton (for monocyclic systems) or to fused nitrogen heterocycles (for fused bicyclic systems). A new class of γ-lactone with a nitrogen heterocyclic skeleton was obtained. Feasible reaction mechanisms involving cascade reactions are presented.     

Macrocyclic Transformations from Norrole to Isonorrole and an N‐Confused Corrole with a Fused Hexacyclic Ring System Triggered by a Pyrrole Substituent

Three kinds of fused porphyrinoids, L2 – L4 , possessing different types of corrole‐based frameworks were synthesized from a pyrrole‐substituted corrole isomer (norrole L1 ). Oxidation of L1 afforded a unique N‐C_meso‐fused pyrrolyl isonorrole L2 , involving the fusion of an auxiliary pyrrolic NH moiety with a meso‐sp³‐hybridized carbon atom. Subsequently, L2 underwent macrocycle transformations to give singly and doubly N‐C_Ar‐fused N‐confused corroles, L3 and L4 , respectively. L3 and L4 contain fused [5.7.6.5]‐tetra‐ and [5.6.7.7.6.5]‐hexacyclic structures, respectively, prepared through lateral annulation. These skeletal transformation reactions from norrole to its isomer isonorrole and finally to N‐confused corrole indicate that multiply fused porphyrinoids could be readily synthesized from pyrrole‐appended confused porphyrinoids.     

Microwave-Assisted Synthesis of Fused Polycyclic Six-Membered N-Heterocycles

The development of new strategies for synthesis of fused polycyclic heterocycles has remained a highly attractive but challenging proposition. An overview of the application of microwave irradiation in nitrogen-containing six-membered fused polycyclic heterocyclic compounds synthesis is presented, focusing on the developments in the past 5 to 10 years. This contribution covers the literature concerning the total synthesis of fused polycyclic N-heterocycles.     

Properties of Bromine Fused Salts Based on Quaternary Ammonium Molecules and Their Relevance for Use in a Hydrogen Bromine Redox Flow Battery

Bromine complexing agents (BCA) in aqueous electrolytes for hydrogen bromine flow batteries are used to reduce bromine‘s vapour pressure, while an insoluble and liquid fused salt is formed. The properties (concentrations, composition, conductivity and viscosity) of this fused salt are investigated in this study systematically ex situ by using 7 BCAs at different state of charge in HBr/Br₂/H₂O electrolytes with a theoretical capacity of 179.6 Ah L⁻¹. Bromine is stored in the fused salt at concentrations up to 13.6 M, reaching theoretical volumetrical capacities up to 730 Ah L⁻¹ in fused salts. The fused salt consists of a pure, bromine- and water-free ionic liquid of organic [BCA]⁺ cations and polybromides, and its conductivity bases on a hopping mechanism among the polybromides. Alkyl side chain length of the BCAs and distribution of polybromides influence strongly the conductivity and viscosity of the fused salts. 1-ethylpyridin-1-iumbromide results to be favoured BCA for application.     

Copper(II)-catalyzed-α-C(sp3)-H activation of cyclic amines: A simple and efficient strategy for the synthesis of fused pyrazole derivatives

In this paper, we have described a simple and efficient strategy for the synthesis of fused pyrazole derivatives. The key steps of our strategy involves hydroamination, copper-catalyzed cross dehydrogenative coupling (CDC) followed by aromatization (aerial oxidation) in one-pot. Our strategy offers a valuable alternative to known methods for synthesis of fused pyrazole derivatives. Overall, we have synthesized 13 diverse fused pyrazole derivatives in moderate to excellent yields.     

Syntheses, structure, and optical properties of ladder-type fused azaborines

[structure: see text] Ladder-type fused azaborines were synthesized. X-ray crystallographic analysis of a pentacene-type molecule shown here revealed the planarity of a fused azaborine. It was revealed by UV-vis and fluorescence spectra that such fused molecular structures are efficient for the extension of pi-conjugated systems containing main group elements.     

Heterocyclic steroids: Synthetic routes and biological characteristics of steroidal fused bicyclic pyrimidines

Natural steroids are characterized as a vital class of compounds, a type of secondary metabolites and components of cell membranes that widely accessible in plants or animals displayed significant pharmacological and varied biological properties. The present study aims to highlight the conveyed researches of synthetic routes adopted to obtain the various structures of steroidal fused bicyclic pyrimidines with substantial biological and pharmaceutical importance. The topic was discussed in light of the synthesis of fused [6 + 5] bicyclic systems, fused [6 + 6] bicyclic systems, binary heterocycles, and biological applications. In detail, the various synthetic strategies for the construction of steroids fused to bicyclic pyrazolopyrimidines, thiazolopyrimidines, triazolopyrimidines, pyridopyrimidines, pyranopyrimidines, and binary pyrimidines were discussed. Heterocyclic steroids of this class of compounds demonstrated potent anticancer, anti-proliferative, anti-neuro-inflammatory, anti-inflammatory, and anti-ulcer activities. It was perceived that the synthetic steroids of such bicyclic pyrimidine scaffolds are fused into the steroid basic skeleton is essential for the potent bioactivities.     

Expanding the porphyrin pi-system by fusion with anthracene

Synthesis of beta,meso,beta-anthracene triply fused and beta,meso-anthracene doubly fused porphyrins has been achieved via oxidative intramolecular ring closure of meso-(9-anthryl)porphyrins and meso-(1-anthryl)porphyrins, respectively. Fusion was only possible when the anthracene carried electron-donating alkoxy substituents. The fused porphyrins exhibit strongly red-shifted UV-vis absorption spectra and reduced electrochemical HOMO-LUMO gaps (relative to the unfused tetraaryl porphyrin precursor).     

Hétérocyclisation de la nor-3 ar-himachalone-9

We report the facile formation of several different three- and five-membered rings fused to the seven-membered ring of 3-nor-arylhimachal-9-one. We also report the formation of several six-membered rings fused to the seven-membered ring of 3-nor-arylhimachal-9-one. However, in these latter instances, the cyclizations were more difficult to accomplish. In fact the yields were generally low. Similar cyclizations to produce heterocyclic seven-membered rings fused to the seven-membered ring of 3-nor-arylhimachal-9-one have not been accomplished.     

One‐Pot Cascade Transformation of Glucal into Structurally Diverse Drug‐Like Scaffolds

A diversity‐oriented synthesis strategy to produce three types of structurally drug‐like N‐heterocyclic‐fused rings has been developed from abundant biomass‐derived d ‐glucal, aniline and water in a stereoselective manner. The overall transformation which entails a cascade of Ferrier reaction and 4π conrotatory imino‐Nazarov cyclization was performed in one‐pot allowing convenient preparation of scaffolds of high molecular complexity from relatively simple starting materials. While indoline‐fused products were readily accessible using ortho‐unsubstituted secondary anilines as substrates, reactions with ortho‐hydroxyl‐anilines furnished fused 1,4‐benzoxazines instead. In both cases, InBr₃ acted as the Lewis acid catalyst. By altering InBr₃ to Ln(OTf)₃, the indoline‐fused products could be further converted into tetrahydroquinoline‐fused cyclopentenones via ensuing retro‐ene rearrangement.     

Heteroleptic Tetrapyrrole‐Fused Dimeric and Trimeric Skeletons with Unusual Non‐Frustrated Fluorescence

Phthalocyanine (Pc) and porphyrin (Por) chromophores have been fused through the benzo[α]pyrazine moiety, resulting in unprecedented heteroleptic tetrapyrrole‐fused dimers and trimers. The heteroleptic tetrapyrrole nature has been clearly revealed based on single‐crystal X‐ray diffraction analysis of the zinc dimer. Electrochemical analysis, theoretical calculations, and time‐resolved spectroscopic results disclose that the two/three‐tetrapyrrole‐fused skeletons behave as one totally π‐conjugated system as a result of the strong conjugative interaction between/among the tetrapyrrole chromophores. In particular, the effectively extended π‐electron system through the fused‐bridge induced strong electronic communication between the Pc and Por moieties and large transition dipole moments in the Pc–Por‐fused systems, providing high fluorescence quantum yields (>0.13) and relatively long excited state lifetimes (>1.3 ns) in comparison with their homo‐tetrapyrrole‐fused analogues.     

The Profound Effect of the Ring Size in the Electrocyclic Opening of Cyclobutene‐Fused Bicyclic Systems

Fused cyclobutenes, prepared by the photocycloaddition of propargyl alcohols to cyclic anhydride chromophores, undergo facile thermochemical ring opening to fused γ‐lactones. The size of the fused ring profoundly influences the temperature that is required to facilitate the ring opening (from 50 °C to 180 °C) and the nature of the product that is formed. Our studies provide new insights into the mechanistic course of these reactions and have been extended to facilitate the preparation of lactams fused to medium‐sized rings.     

Synthesis of 3,4‐Fused Tricyclic Indoles Using 3‐Alkylidene Indolines as Versatile Precursors

In this personal account, our recent studies of novel synthetic methods of 3,4‐fused tricyclic indole derivatives using 3‐alkylidene indoline derivatives as versatile precursors are discussed. Two types of cascade reactions producing 3,4‐fused tricyclic 3‐alkylidene indolines were developed based on a palladium‐catalyzed intramolecular Heck insertion to an allene‐allylic amination cascade and a platinum‐catalyzed intramolecular Friedel‐Crafts type C?H coupling‐allylic amination cascade. Furthermore, three types of 3,4‐fused tricyclic indoles were accessible from a single 3‐alkylidene indoline precursor via acid‐promoted olefin isomerization or oxidative treatments. The application of the developed methods to the synthesis of natural products bearing a 3,4‐fused tricyclic indole skeleton, (?)‐aurantioclavine, fargesine, and synthetic studies of dragmacidin E are also highlighted.     

Synthesis of γ-butyrolactone fused cyclooctene

The expeditious route for the synthesis of γ-butyrolactone fused cyclooctene starting from the γ-butyrolactone fused cyclopentane through bicyclo[4.2.1]nonan-9-one is reported. Retro-Dieckmann’s condensation of bicyclo[4.2.1]nonan-9-one in presence of sodium methoxide and methanol furnished γ-butyrolactone fused cyclooctene in good yield. Surprisingly, the stereochemistry of ring-junction of γ-butyrolactone fused cyclooctene is different from the γ-butyrolactone fused cyclopentane, and the position of new ester group, which were confirmed unambiguously by X-ray analysis.     

Synthesis of hexacyclic fused isocoumarin framework through selective domino multicyclizations under catalyst and solvent free conditions

A novel fused isocoumarin skeleton has been synthesized through selective domino multicyclizations by mixing homothallic acid and 2,3-diphenylacryloyl chloride at 200℃ under catalyst and solvent free reaction conditions. Six fused rings with two stereogenic centers were assembled in a convenient onepot operation in good yield. The resulting hexacyclic fused isocoumarin skeleton and its stereochemistry was fully characterized and unambiguously confirmed by X-ray diffraction analysis.     

Theoretical studies on graphyne substructures: geometry, aromaticity, and electronic properties of the multiply fused dehydrobenzo[12]annulenes

The geometries of multiply fused dehydrobenzo[12]annulenes [12]DBAs 2-7 with various topologies, which are considered as graphyne fragments, have been optimized at the B3LYP/6-31G* level of theory. Most of the optimized geometries of fused DBAs have planar structures excluding a boomerang-shaped bisDBA 4, a trefoil-shaped trisDBA 6, and a wheel-shaped DBA 7. For the boomerang-shaped bisDBA 4 and the trefoil-shaped trisDBA 6, distortions originate from the steric repulsion between hydrogen atoms attached to adjacent benzene rings. The harmonic oscillator model of aromaticity (HOMA) values at the central benzene ring of multiply fused DBAs decrease as the number of fused 12-membered rings increases except for the closely related structures 4 and 5 and 6 and 7, because of bond length elongation due to conjugation with the phenylethynyl groups. Nucleus-independent chemical shifts (NICS) were computed at the individual ring centers of the fused DBAs. The fusion of the antiaromatic 12-membered rings results in increasing (more positive) NICS values at the central benzene ring, indicating the decrease of diatropic ring currents. Furthermore, HOMO-LUMO gaps of the DBAs 2-7 are strongly influenced by the molecular topology. The para-conjugation pathway of the bis(phenylethynyl)benzene unit plays a more important role in the determination of the electronic properties of multiply fused DBAs than the meta- and ortho-conjugation pathways.